Abstract OT2-07-06: Phase Ib study to assess the safety, tolerability, and clinical activity of gedatolisib in combination with palbociclib and either letrozole or fulvestrant in women with metastatic or locally advanced/recurrent breast cancer (B2151009)

Preclinical evaluation of the CDK4/6 inhibitor palbociclib in combination with a PI3K or MEK inhibitor in colorectal cancer

BACKGROUND

Studies have demonstrated the efficacy of Palbociclib (CDK 4/6 inhibitor), Gedatolisib (PI3K/mTOR dual inhibitor) and PD0325901 (MEK1/2 inhibitor) in colorectal cancer (CRC), however single agent therapeutics are often limited by the development of resistance.

METHODS

We compared the anti-proliferative effects of the combination of Gedatolisib and Palbociclib and Gedatolisib and PD0325901 in five CRC cell lines with varying mutational background and tested their combinations on total and phosphoprotein levels of signaling pathway proteins.

RESULTS

The combination of Palbociclib and Gedatolisib was superior to the combination of Palbociclib and PD0325901. The combination of Palbociclib and Gedatolisib had synergistic anti-proliferative effects in all cell lines tested [CI range: 0.11-0.69] and resulted in the suppression of S6rp (S240/244), without AKT reactivation. The combination of Palbociclib and Gedatolisib increased BAX and Bcl-2 levels in PIK3CA mutated cell lines. The combination of Palbociclib and Gedatolisib caused MAPK/ERK reactivation, as seen by an increase in expression of total EGFR, regardless of the mutational status of the cells.

CONCLUSION

This study shows that the combination of Palbociclib and Gedatolisib has synergistic anti-proliferative effects in both wild-type and mutated CRC cell lines. Separately, the phosphorylation of S6rp may be a promising biomarker of responsiveness to this combination.

Emerging data and future directions for CDK4/6 inhibitor treatment of patients with hormone receptor positive HER2-non-amplified metastatic breast cancer

Cyclin-dependent kinase (CDK4/6) inhibitors in combination with endocrine therapy are currently the optimal first line treatment for hormone receptor (HR) positive, human epidermal growth factor receptor 2 (HER2) non-amplified metastatic breast cancer (MBC). However, not all patients benefit from this treatment and all patients will inevitably progress. Identifying therapeutic strategies in this setting is therefore of immediate clinical importance. We present an overview of the mechanisms of resistance to CDK4/6 inhibitors and review potential biomarkers that may guide therapy selection. We also discuss the use of CDK4/6 inhibitors in the context of non-HR-positive/HER2-non-amplified breast cancer and in combination with therapies other than endocrine therapy.

Overcoming endocrine resistance in metastatic hormone receptor-positive breast cancer

Endocrine therapy has historically formed the basis of treatment of metastatic hormone receptor-positive breast cancer. The development of endocrine resistance has led to the development of newer endocrine drug combinations. Use of the CDK4/6 inhibitors has significantly improved progression-free survival in this group of patients. There are multiple studies of the use of P13K inhibitors and mTOR inhibitors for use as subsequent lines of therapy, particularly for endocrine resistance. The optimal sequencing of therapy should be based on medical comorbidities, prior adjuvant therapies, quality of life, side-effect profile, and disease-free interval.